SAN DIEGO — A technology industry executive and former state assemblyman conceded defeat on Wednesday in the race for San Diego mayor and endorsed a fellow Democrat and city councilman.

Nathan Fletcher said he supports David Alvarez in a runoff against Kevin Faulconer, a Republican city councilman.

The election was held to replace Bob Filner after he resigned amid allegations of sexual harassment.

Fletcher was trailing Alvarez by 1 percentage point for second place with tens of thousands of ballots remaining to be counted.

Faulconer easily topped the field of 11 candidates with 46 percent of the votes cast in Tuesday's vote but fell short of the majority needed to avoid a runoff.

His strong showing gives Republicans a chance to recapture an office they held for much of the past four decades and an opportunity for a rare win leading a major American city.

Alvarez, riding support from organized labor and an effort to turn out voters in heavily Latino neighborhoods, followed with 25.6 percent.

Fletcher, an executive at wireless technology titan Qualcomm Inc. and former state assemblyman, was trailing with 24.3 percent.

With no one winning a majority, the top two finishers advance to a runoff. About 34,500 mail-in and provisional ballots remained to be counted out of nearly 240,000 votes cast. Fletcher would have to get a far larger percentage of the remaining ballots to overcome the deficit, an unrealistic possibility.

Faulconer, a former public relations executive, must appeal well beyond his Republican base to prevail in a runoff, which will likely be scheduled in February. Democrats hold a 13-point advantage over Republicans in voter registration, and Barack Obama trounced Mitt Romney by 25 points among city voters in last year's presidential election.

"It's not about being a Republican or Democrat. It's about coming together to put San Diego first," Faulconer told supporters.

Filner, the city's first Democratic leader in 20 years, resigned less than nine months into a four-year term after nearly 20 women publicly identified themselves as targets of his unwanted advances, including kissing, groping and requests for dates. He pleaded guilty last month to one felony count of false imprisonment and two misdemeanor counts of battery for his behavior toward women during his brief time in office.

The former 10-term congressman was barely mentioned in campaign mailers or televised debates, but candidates adopted his successful campaign mantra of pouring more money into neglected neighborhoods, promising to repair crumbling streets and sidewalks and faster fire and ambulance response times.

Alvarez was backed by the San Diego County Democratic Party Central Committee and the San Diego and Imperial Counties Labor Council, the largest coalition of organized labor.